1. field of the Invention
The present invention relates to an optical functioning glass doped with Nd.sup.3+, and to an optical fiber, a waveguide device, and an optically active device, all of which use this optical functioning glass.
2. Related Background Art
Efforts have been made to manufacture an optically active device such as a fiber amplifier, a fiber sensor, and a fiber laser by using a glass doped with a rare-earth element for the application to a light communication at a 1.3-.mu.m wavelength band and the like. For example, a report has been made (ELECTRONICS LETTERS, 1990, Vol. 26, No. 2, pp. 121-122) in which an optical functioning glass is prepared by adding neodymium ions (Nd.sup.3+) as an active ions to a phosphate glass as a host glass, an optical fiber is formed from this optical functioning glass, and laser oscillation characteristics of the optical fiber are evaluated. It reports about the optical fiber characteristic that a fluorescence peak wavelength caused by Nd.sup.3+ was about 1.32 .mu.m, an absorption peak wavelength caused by ESA (excited state absorption) transition was about 1.31 .mu.m, and an oscillation peak wavelength was about 1.36 .mu.m.
However, in the reported optical fiber, a sufficiently high laser oscillation gain cannot be obtained because the absorption peak at the wavelength of 1.31 .mu.m is present near the fluorescence peak at the wavelength of 1.32 .mu.m, and because the intensity of the absorption peak at the 1.31-.mu.m wavelength band is higher than that of the fluorescence peak at the 1.32-.mu.m wavelength band.
In addition, since the absorption peak exists at a wavelength shorter than that of the fluorescence peak, the oscillation peak wavelength is shifted to a wavelength longer than the 1.3-.mu.m wavelength band. As a result, a substantial gain of laser oscillation cannot be obtained at the 1.3-.mu.m wavelength band.